Considerable evidence indicates that T cells are important in the immunopathogenesis of rheumatoid arthritis. The major goals of our current studies are to characterize the T cell receptors (TCRs) expressed by clonal CD4+ T cell expansions in the synovial fluid of patients with rheumatoid arthritis and to determine whether these clones are also present in paired samples of another joint of the same patient and in the blood. Additional studies will examine whether these clonal expansions and other specifically expanded T cells are present at later time points. Finally, the TCRs expressed by these clonal expansions will be expressed in T cell hybridomas in order to determine the specificity of these T cells for synovial antigens. In the recent funding period, we have analyzed TCR b-chain (TCRB) sequences in two joints and blood of an additional four patients. Despite marked heterogeneity of the synovial T cell receptor sequences, the results showed that 20-30% of the TCRB sequences found in one joint were also expressed in a second joint but not in peripheral blood T cells of the same individual. Analysis of TCRB complementarity determining region 3 (CDR3) sequences showed the presence of multiple clonal expansions. The same oligoclonal expansions were apparent in both joints of the same patient. A few of the expansions were very large (> 30% of the repertoire within a particular TCRBV subset). Continued analysis of the TCR b-chain and a-chain repertoire showed remarkable homology among clones within an individual patient, strongly suggesting selection by the same synovial antigen. However, we have yet to find the same or highly homologous TCRs among different patients. Together, these studies suggest that a significant proportion of synovial CD4+ T cells have been selected and expanded by conventional antigens in this disease. Hybridomas expressing RA synovial TCRs have been generated, and we are currently screening for responses to candidate synovial antigens and peptides.